1. Field of the Invention
The present invention relates to a clear view screen, and more particularly, pertains to a clear view screen in which a rotating frame is floated by air within a fixed frame so as to be rotated.
2. Description of the Prior Art
A clear view screen is provided in a side wall of a ship and the like or in a windshield of a wheelhouse so that waterdrops etc. adhering to the clear view screen are removed by centrifugal force caused by rotation of a glass plate.
FIG. 1 is a partial, sectional front view showing an example of a conventional clear view screen 1. FIG. 2 is a partial sectional view taken along the line II--II in FIG. 1. FIG. 3 is a partial perspective view of a fixed frame 5 for showing air blowing holes 15, where portions unnecessary for explanation are omitted.
In the structure shown in the drawings, the conventional clear view screen 1 comprises, in principle, a fixed frame 5 provided in a windshield 3 and the like of a ship etc., a rotating frame 7 provided rotatably with a gap 13 within the fixed frame 5 and equipped with a transparent plate 9 such as a glass plate, an air blowing means including air blowing holes 15 for blowing air into the gap 13 to float the rotating frame 7 within the fixed frame 5 and an induction motor 22 for driving the rotating frame 7 raised in the fixed frame 5.
In more detail, a fixed frame 5 is provided in the windshield 3 of a ship and the like. As shown in FIG. 2, the fixed frame 5 is cylindrical, having a hollow inner peripheral surface 6 with a V-shaped vertical section. Within the fixed frame 5, a rotating frame 7 is disposed. The rotating frame 7 has a protruding outer peripheral surface 8 with a V-shaped vertical section, which corresponds to the inner peripheral surface 6 of the fixed frame 5. The rotating frame 7 is contained in the fixed frame 5 with a gap 13 left between the outer surface 8 of the rotating frame 7 and the inner surface 6 of the fixed frame 5. Accordingly, the rotating frame 7 is rotatable in a plane extending from a transparent plate 9. In order to decrease the rotational resistance of the rotating frame 7, that is, the frictional resistance between the inner surface 6 of the fixed frame 5 and the outer surface 8 of the rotating frame 7, the rotating frame 7 is floated within the fixed frame 5 by the force of air supplied by the air blowing means.
Now, description will be made of the air blowing means. A plurality of air blowing holes 15 are formed at equal distances along the circumference of the fixed frame 5. One end of each air blowing holes 15 is opened to the gap 13 and the other end thereof is connected with a compressor or a blower (not shown) through an air supply pipe 17. Accordingly, compressed air from the compressor or the blower is sent to the air blowing holes 15 through the air supplying pipes 17 so as to blow forcefully into the gap 13 from the air blowing holes 15. The air blowing holes 15 are structured such that air blows to float the rotating frame 7 in a well balanced manner. More particularly, as shown in FIGS. 2 and 3, compressed air is made to blow into the gap 13 from the opposingly inclined planes of the inner surface 6 of the fixed frame 5 so that undesirable forces, that is, component forces applied perpendicularly to the rotating surface of the rotating frame 7 can be cancelled. The rotating frame 7 thus floated within the fixed frame 5 is made to rotate by an induction motor 22 used as a driving means, which will be described below.
In the induction motor 22, the fixed frame 5 serves as the stator side and the rotating frame 7 serves as the rotor side. More particularly, in the fixed frame 5, a stator core 23 is provided along the circumference of the fixed frame 5. A stator winding 25 is set around the stator core 23. Accordingly, when an alternating current is made to flow through the stator winding 25, a revolving magnetic field is generated due to the co-operated interaction with the stator core 23. On the other hand, in the rotating frame 7, a cylindrical rotor core 27 is provided in a coaxial circle with respect to the rotating frame 7. Further on the rotor core, a copper plate cylinder 29 is provided. The stator core 23 on the fixed frame 5 and the copper plate cylinder 29 on the rotating frame 7 are disposed with a small distance and thus, the rotating frame 7 is rotated by the action of the above described revolving magnetic field.
In operation, the compressor or the blower is operated to send air to the air supplying pipes 17. Air sent to the air supplying pipes 17 is made to blow forcefully into the gap 13 through the air blowing holes 15. Air forcefully blown into the the gap 13 is struck against the outer surface of the rotating frame 7 to cause a force to react. This force reacts in a direction in which the rotating frame 7 would move away from the fixed frame 5, and as a result, the rotating frame 7 is floated within the fixed frame 5. As described above, component forces applied in the undesirable directions are cancelled by each other by means of the two opposite air blowing holes 15 (see FIGS. 2 and 3). Thus, the rotating frame 7 is supported rotatably in a well balanced manner within the fixed frame 5.
Then, the driving means is operated. More specifically, an alternating current is supplied to the stator winding 25. The stator winding 25 through which alternating current flows interacts with the stator core 23 so as to generate a revolving magnetic field, which passes through the copper plate cylinder 29 and attains the rotor core 27 provided inside the cylinder 29. As a result, an electric current is generated in the copper plate cylinder 29 and by the action of this electric current and the above described revolving magnetic field, the rotating frame 7 is rotated. An arrow A in FIG. 1 shows an example of a rotating direction. In the above described manner, the rotating frame 7 rotates, and simultaneously a transparent material 9 provided in the rotating frame 7 rotates together, so that waterdrops and the like on the transparent material 9 can be removed by centrifugal force. Thus, excellent visibility through a clear view screen can be assured.
However, in a clear view screen as structured above, it is needed to blow a sufficient amount of air into the gap 13 in order to float the rotating frame, and as a result, a large number of small air blowing holes 15 must be formed at equal distances in the fixed frame 5, which makes the manufacture of the fixed frame 5 complicated. In addition, since air is made to blow from the discontinuous portions such as the air blowing holes 15, discontinuous air layers are generated in the gap 13, and in certain areas apart from the air blowing holes 15, the amount of air emitted from the gap 13 to the outside OUT decreases. As a result, it is feared that water and the like will infiltrate into the inside IN of the clear view screen from the outside OUT of the clear view screen through the gap 13. Furthermore, air is forced to pass through the air blowing holes 15 small-sized in section, which causes an increase in atmospheric pressure in the air supply pipes, and accordingly, the pressure of the compressor or the blower must be increased in order to supply air. Therefore, a clear view screen in which the above described disadvantages can be overcome has been desired.